For inner walls and ceilings of architectural structures, well-designed wallpapers in the form of sheets are widely used. The wallpaper is generally made of incombustible base paper or non-woven fabric to give sticking property, incombustibility, and fireproof property to the wall surfaces. The wallpaper also has a resin layer on its surface to give resistance to scratch and contamination. The resin layer is composed mainly of a polyvinyl-chloride-based resin containing an ester-oil-based plasticizer. The resin layer further contains a foaming agent that gives flexibility upon foaming. It is widely known that a three-dimensional decoration can be given to the resin layer by embossing.
Recently, many attempts have been made to print a desired image on such a resin layer by inkjet printing system and to apply the resin layer to wallpapers. However, there is a problem that vinyl chloride is very poor at absorbing ink for its material characteristics. To solve this problem, PTL 1 has made an attempt to provide an ink receiving layer on the resin layer composed of vinyl chloride to accelerate permeation and fixation of ink thereto.
A similar attempt has been made in PTL 2 using an oil-based ink. Oil-based ink advantageously provides a high-density image since colorants are dissolved or dispersed therein at a high concentration. Oil-based ink also has excellent resistance to water and nozzle clogging in inkjet apparatuses. Also, having excellent resistance to light and ozone, oil-based inks are widely used for wallpapers applied for large-size POP art, advertisement, and display.
Since the major ingredient is a nonvolatile oily component, oil-based ink has very poor permeability and absorptivity to the resin layer. To solve this problem, PTL 2 has attempted to form an oil-based ink receiving layer composed mainly of a vinyl chloride-acrylic resin copolymer having a desired glass transition temperature on a support, to increase the number of cracks appearing on the surface of the resulting wallpaper and accelerate permeation of ink thereto.
With respect to the method described in PTL 1, provision of the ink receiving layer disadvantageously makes the production process of wallpaper more complicated and the production cost thereof much higher.
The method described in PTL 2 is the same as that described in PTL 1 in that the ink receiving layer is provided to improve ink fixability. However, these methods do not improve inkjet printing quality on wallpapers which are composed of soft vinyl chloride that is generally and widely used.
In view of this situation, there is a demand for an improved inkjet printing method which can print high-quality images on soft vinyl chloride with an ink having high permeability, to produce wallpapers in a simple process.